Re-Installing from CE Disc?

[SEE]

My install has a developed a serious problem - verifying cache hasn't worked despite showing 20 files in need of replacement and replacing them - I still have serious gameplay issues that have suddenly appeared and I cannot resolve them.

I need to re-install CloD but what is the correct procedure, the threads I have found also relate to re-installing Steam which I don't think is necessary for me.

I have backed up my custom missions/campaigns/folders etc, config/User ini files,etc. Thanks for any help!